(a) Field of the Invention
This invention relates to a method for the installation of an elastomeric gasket in the peripheral surface of an opening through the body of a manhole wall.
(b) Description of the Prior Art
The construction of concrete manholes is heavy, dirty work and the men who engage in this type of work are usually classified as unskilled labour, the use of the pre-case base having a pipe section precast therein and pre-sealed thereto have also been proposed heretofore. Such pre-sealed structures lack the flexibility needed to accommodate changes that are frequently dictated by conditions encountered in the field and which are not known at the time the installation is in the design or planning stage. Hence it is advantageous if a method that is devised for sealing the annular opening between sewer pipes and concrete manholes is simple, inexpensive and easy to follow and use.
When forming openings in poured concrete structures it is necessary to permit ample time for the concrete to set to a relatively rigid condition, before the apparatus used to form the opening in the concrete wall can be removed. Clearly, the longer the setting time, the more forms that must be used in order to enable the concrete objects to be produced on a mass production basis. Conversely, the shorter the curing time, the lower the capital investment that must be made in terms of forms, opening forming inserts, and the like. If the opening forming inserts are removed too soon, before the concrete is sufficiently set, the rubber gasket being set in the concrete opening may be jarred or moved prematurely, and consequently the water-tightness of the seal may be broken, Furthermore, in a heavy business like the concrete pouring business, and with concrete being a good fastening agent, it is frequently necessary to use a sledge hammer or some other heavy object to break loose an insert forming an opening in a concrete wall. These heavy removal techniques contribute to the probability that the seal formed in place in the poured concrete will be jarred in a manner which breaks the water-tightness of the seal.
While it is important to keep the interior of a manhole reasonably dry, this has proved to be a difficult objective to accomplish where pipes pass through a manhole wall. Concrete cannot economically be installed with precisely smooth surfaces. Gaskets and other seals are not always effective in situations of this type. Too often water seeps past them, where irregularities, holes or humps are present in the concrete.
The sealing methods and seal constructions heretofore used are generally time consuming in appliction, and thus require that ample curing time be given to the concrete before forms can be removed. Long curing times for poured concrete, particularly in mass production situations, increases the cost of manufacture of the poured concrete forms. Furthermore, complicated pouring techniques tend to increase the cost of the poured concrete structures.
One proposed sealing technique has been the installation of O-rings between suitably shaped collars which surround the pipe and mate with the inner surface of the opening through which the pipe passes. This has not been entirely successful, however, for minor imperfections in the concrete will permit the seepage of moisture past the O-ring gasket. Furthermore, such a gasket must be tight along at least two lines of contact, and this doubles the problem of avoiding irregularities and roughness at any point which comes in contact with the O-ring. Since the O-ring is solid, it is not easily forced into different shapes in order to conform to local irregularities in the surface or to imperfections in concentricity. Since the O-ring can roll upon itself, it needs extraneous fittings to make it stay in place.
Because of the conditions under which sewer pipe is installed, it frequently happens that a section of pipe will lie at an angle to the overall axis of the pipe, due to subsidence in a muddy trench, lack of care in back filling, or any of numerous other causes. When such a condition arises and affects a section of pipe which is to pass through the wall of a manhole, it is quite important that the opening through which the pipe passes should be so constructed as to allow for variations in alignment.
As noted hereinbefore, it has been proposed to use molded gaskets of elastomeric material and shaped like an ordinary washer. Such washers are embedded in concrete about their outer margin, and lie normal to the axis of the pipe. They are subject to the disadvantage that the elastomer used has limited stretch in radially outward direction. That is, even though it can be made with an undersize hole, so that the pipe will stretch the material on being inserted, the amount of stretch is not sufficient, in the plane of the gasket, to provide enough freedom for distortion to preserve a tight seal.
The shear stress imposed on sewer pipe passing through a manhole opening may be very severe. Sometimes it is sufficiently substantial to break the pipe right off. If the load, including not only the weight of the pipe and is contents, but also that imposed by fill, traffic stress, and vibration, is great, the pipe will be driven down into the inner edge of the rubber in the lower part of the gasket, directly under the pipe, and the amount of compression may be sufficient to cause the top of the pipe to pull away from the inner upper edge of the gasket, thus leaving a small opening between gasket and pipe. If the elasticity of the elastomeric material is sufficient to ensure that its upper rim will follow the pipe even under the stress conditions stated, it is probably so "tight" that insertion of the pipe is practically impossible. This factor is important, for the choice of elastomeric material is limited. The ASTM specifications for rubber gasketed sewer pipe are quite strict. The elastomer usually conforms to ASTM 13, SBR 1200, or to ASTM 361, Polystyrene, TS 2400.
If the embedded portions of the gasket are planar and extend in a normal direction away from the pipe, they may be pulled right out of the concrete in which they are embedded, under stress of axial movement of the pipe.
One problem which faced the prior art was to provide an improved technique for positively and permanently anchoring the gasket in the cementitious material which defines the inner surface of the opening. The problem did not appear to be solvable by the use of individually molded unitary gasket washers ["washers" as used herein, refers to centrally-apertured articles of disk-like shape], sine they lack sufficient resistance to compression in their lower, inner portion, which carries the major load, and were too subject to peripheral separation from the pipe in their upper portions. Furthermore, such washers would have to be stocked in many sizes.
Several other proposals have been made in the past in Canadian Pat. No. 964, 043, issued Mar. 11, 1975, to Harry W. Skinner, disclosed an apparatus and method to support a rubber-sealing ring or gasket in position while a concrete structure is cast thereabout, the apparatus serving to define an opening in the concrete structure and to support the rubber-sealing ring in position while the concrete was formed thereabout in securing relation. The rubber seal was an elaborate and expensive generally V-shaped rubber sealing ring, which was fitted between the circular opening in the manhole and the pipe penetrating into the interior of the manhole. The sealing qualities of the rubber seal were said to be enhanced by applying outward pressure on the arms of the V-shaped seal by driving a wedge-shaped material into the space existing between the arms of the V-shaped seal. This system was relatively successful but the V-shaped seal was prone to ripping or tearing when the pipe was introduced into the interior of the manhole.
Canadian Pat. No. 971,997, granted July 29, 1975, to John Ditcher, provided a method for installing a sealing member which yieldingly spans the annular space between the exterior surface of a sewer pipe when it passed through the opening in the wall of a manhole, and the inner surface of the opening through which the pipe passed. Ditcher disclosed an A-shaped sealing ring, of a particular specified cross-sections. This A-shaped seal performed reasonably well but was prone to breaking because of its hollow-core construction. Further, the two legs of the A-shaped seal were rather widely angled, and this construction, when the A-shaped seal was distorted by inserting the pipe through the opening in the manhole, tended to place considerable lateral and upward pressure on the two legs of the seal, with the result that one or both of the two legs broke free from the concrete in which the legs are embedded.
The invention provided in Canadian Pat. No. 971,997, issued July 29, 1975 to John Ditcher also provided a method for installing a sealing element for use between the outer surface of a pipe and an opening in a wall through which the pipe passes. The method included casting a wall of settable material about a particularly described shaping member. The shaping member was provided with means defining a peripheral channel to engage a peripheral gasket ring of resilient material and to house a substantial portion only of the ring. A remaining portion of the ring was left extending into the settable material as it is being emplaced. The material was allowed to set and thereafter the shaping member was removed. This was said to provide a sealing member within the manhole opening.
The invention in Canadian Pat. No. 996,150 issued Aug. 31, 1976 to John Ditcher provided a gasket for sealing the space between a pipe and the surrounding surface of an opening through which the pipe passed. The gasket was composed of elastomeric material, having, throughout its extent, a uniform cross-section. The gasket is made from an extruded rubber strip, having a cross section in the shape of a capital A. When properly positioned in the manhole opening, the apex of the A was exposed, and extended radially inwardly to make first contact with the surface of the pipe. The legs of the A extended outwardly, and were embedded in cementitious material which lined the opening in the manhole wall. There was some difficulty in installation because the elastomeric gasket was made from an extrusion in the cross-sectional form of a capital A, and hence it required some distortion of the gasket, to fit this gasket onto the mold rings.
Canadian Pat. No. 1,018,331, issued Oct. 4, 1977, to Ronald E. Yoakum, disclosed a means of automatically affecting a seal at the junctures between a manhole and its inlet and/or outlet sewer pipe connections by the use of a seal. It also taught a method of installing the seal. A complex shaped elastomeric annular sealing means was positioned circumferentially within the opening in the manhole, was intricately connected to the wall portion of the manhole and was adapted for automatically engaging the sewer pipe which was inserted through the manhole opening. The seal provided a connection which was purportedly water proof. The Yoakum seal was rather complex in construction and hence both expensive and difficult to install. The construction of the seal involved a number of grooves and projections, and hence because of the nature of poured concrete which does not flow readily into small corners and openings, it was difficult to obtain a water-tight seal, particularly when the dry casting technique of pouring concrete was used.
The invention in Canadian Pat. No. 1,073,938 issued Mar. 18, 1980 to John Ditcher provided a molded elastomeric gasket for resiliently supporting a sewer pipe in a manhole opening and sealing the space between the wall of the opening and the surface of the pipe. The gasket had an outer cylindrical flange member connected to a main bulbous body portion by a composite inwardly directed annular web and an outwardly directed annular web. The main body portion was integrally connected to region of the inner surface of the cylindrical flange member and integral a "T" cross-section head which was to be embedded in the material lining the manhole opening.
The invention in Canadian Pat. No. 1,077,692 issued May 20, 1980 to John Ditcher was based on the discovery that a seal having all of the desired properties could be made by utilizing an extrusion having a pipe-contacting part which, instead of being of A-shape was pear-shape in section and was unitarily provided with a T-shaped anchoring part, the stem of the T being united with the bottom of the pear-shaped part and affording, when longitudinally considered, a web of substantial height and thickness. Such an extrusion can be used effectively only if handled in the complex manner specifically set forth.
The invention in Canadian Pat. No. 1,079,993 issued June 24, 1980 to Dominique Palazzo provided a sealing system, and a method of installation therefor, whereby the annular opening existing between an opening through the wall of a concrete manhole, and the inlet-outlet connection of the sewer pipe or conduit could be effectively and inexpensively sealed in a water-tight manner, to eliminate infiltration and/or ex-filtration of liquids into and out of the manhole. The seal provided was said to be of sufficient flexibility in construction and design that it would be capable of continuing to maintain a water-tight seal between the manhole and the conduit, even when the manhole-conduit combination is subjected to significant degrees of distortion due to shifting earth, and relative mis-alignment occurs between the manhole opening and the conduit. The anchoring legs were subject to stress and strain, and, even though they were firmly embedded in the concrete, were subject to breakage at their flexive points, thus being prone to leakage.
The invention in Canadian Pat. No. 1,112,468 issued Nov. 17, 1981 to F. Poulette provided a method for installing a gasket in the peripheral wall of an opening in a masonry wall which involved a particularly complicated series of steps using special complicated apparatus. The installing step required a high degree of expertise and adjustments for deficient sizes was difficult.
Typical seals were also disclosed in U.S. Pat. Nos. 2,924,427; 2,935,349; 3,348,850 and 3,832,438. Such annular seals were secured in place either by frictional contact with the walls defining the clearance or in the alternative by auxiliary clamping devices assembled to the pipe or to the concrete structure. Such sealing arrangements suffered from the disadvantage of being difficult and time consuming to install as well as being subject to leakage or blowout.
Another example of such gasket is shown in U.S. Pat. No. 3,832,438, issued Aug. 27, 1974. That gasket consists generally of a peak portion which engages the pipe and a leg portion which is embedded in concrete around the peripheral wall of the opening. In the above patent, the peak portion of the gasket is positioned in a recess formed between the mating edges of two oppositely tapered metal molds. The molds are mounted between the walls of a form and concrete is poured between the walls to embed the leg portion of the gasket in the peripheral wall of the opening when the concrete is set.
Another prior art gasket is embedded in the wall of the riser and projects inwardly of the opening through the riser to engage the outer surface of the intersecting feed pipe. The gasket is made of a resilient material which permits the gasket to yield and form a tight seal when the intersecting pipe is thrust into position.
The invention in U.S. Pat. No. 3,727,876, issued Apr. 17, 1973 to L. R. Keyser provided a three-piece assembly for the installation of the seal. The assembly includes inner and outer mold members, and a ring-shaped sustaining plate. Thus, this patent provided apparatus for forming a void through a molded wall during fabrication thereof and supporting a gasket for embedment in the wall about the void.
The invention in U.S. Pat. No. 3,758,066, issued Sept. 11, 1973 to H. W. Skinner et al provided an apparatus and method for forming a pipe joint sealing device which serves the dual purpose of supporting a rubber-sealing ring in position while concrete was cast thereabout and also for defining the opening into which the sealing ring is installed. This mold device included plug structure of particular specification. Here, too, the major problem was of easy adjustability. This patent suffered the deficiency that adjustments for different locations of the manhole openings were difficult.
The invention in U.S. Pat. No. 3,759,285, issued Sept. 18, 1973 to R. E. Yoakum provided an in situ seal in a hole in the wall of a manhole which was said to permit independent movement of either the pipes or the base to maintain the seal and yet to accommodate changing job conditions. However, because of the embedment means within the concrete, the seal could be worked lose and hence cause leakage.
The invention in U.S. Pat. No. 3,787,061, issud Jan. 22, 1974 to R. E. Yoakum provided an in situ seal in a hole in the wall of a manhole in which the pipe engaging portion was a pair of spaced apart ribs, releasably biased inwardly but adapted to be flattened into sealing engagement with the pipe. Such flattening did not always, however, provide a continuous water-tight seal if there were movement or misalignment of the pipe or manhole.
In the invention in U. S. Pat. No. 3,874,063, issued Apr. 1, 1975 to F. W. Skinner et al a pipe joint sealing device is provided which includes an annular resilient body of rubber-like material. This body is generally a V-shaped cross-section which includes radially inner and outer annular body portions or flanges which is secured to the hole in the wall of the manhole by casting or molding concrete around the outer periphery or flange of the sealing ring such that when the concrete hardens, the ring is locked into position. A major deficiency is that, in order to effect a seal between the concrete manhole and the pipe a wedge of rubber material must be inserted into the space between the inner and outer flanges.
The invention in U.S. Pat. No. 4,333,662 issued June 8, 1982 to William D. Jones provides a gasket which is particularly suited for sealing the annular space between a pipe and a port in an underground structure is disclosed. The gasket comprises a hollow annular ring which surrounds the pipe and is connected by a narrow neck to a base at least partially embedded in the underground structure. The base has means extending around its outer periphery to mount the seal securely in the manhole and to provide a block against water seepage across the periphery of the gasket.
The invention in U.S. Pat. No. 4,387,900 issued June 14, 1983 to Jack Ditcher et al provides a resilient gasket having an outer annular flange positioned within a manhole opening and maintained thereagainst under compression by means of a compression band. The gasket is provided with a central opening defined by an enlarged beaded periphery having an elasticity adapted to tightly encircle the outer periphery of the pipe. A folded intermediate section is arranged between and integrally joined to the outer flange and the beaded inner periphery. The intermediate section is comprised of first and second diagonally annular portions integrally joined along a fold to define a V-shape which imparts a yieldability enabling the gasket to maintain a watertight seal between the manhole opening and the pipe, even in the presence of a significant misalignment therebetween. A strap is positioned about the intermediate section of the gasket adjacent the inner beaded periphery to enhance the water-tight seal between the gasket and the pipe. The compression band may be provided with pairs of substantially V-shaped slots which enable the band to assume a curvature in a direction transverse to the curved periphery in order to conform to the curvature of the manhole opening. The clamping band is formed of a material which is impervious to the surrounding environment and has a gap and a segment hingedly connected to the main body thereof for placement in the gap and against the interior surface of the gasket to lock the compression band in position and maintain the gasket flange under compression. An expansion assembly includes an expansion ring which cooperates with a hydraulic jack and is positioned against the compression band to expand the compression band into position against the gasket flange and to apply a force uniformly around the compression band to insure proper positioning and locking of the clamping band.